U.S. Pat. No. 6,656,391 discloses a process for preparing a castable powder of uranium dioxide (UO2) for the use in the manufacture of MOX fuels. The process includes spray drying of a flowable UO2 powder obtained by dry process conversion of uranium hexafluoride (UF6).
U.S. Pat. No. 6,352,677 discloses a process to produce commercial grade anhydrous hydrogen fluoride (AHF) and UO2 from the defluorination of UF6.
U.S. Pat. No. 5,346,684 discloses a method for recovering an anhydrous hydrogen fluoride from depleted UF6.
U.S. Pat. No. 4,830,841 discloses a UF6 to UO2 dry conversion reactor. Such a conversion is currently done in a single segment reactor with a gas-phase reaction section and a defluorination/agglomeration section which are fixed for running up to the enrichment level required in commercial light water reactors to produce a controlled nuclear reaction, i.e. up to a maximum enrichment of 5% U-235. The upper portion of the reactor separates the solid from the gas phase using sintered metal filters. The UO2F2 is defluorinated and the UO2 is agglomerated in the lower portion of the reactor using a fluidized bed. Both the fixed fluidized bed and gas-phase reaction sections geometries do not allow for timely or cost effective changes to capacity or U-235 enrichment, or ease of maintenance.
Current dry conversion reactors are usually made of material typically used in high temperature applications such as nickel-chromium based superalloys, e.g. Inconel®625, or of material resistant to corrosion such as nickel-copper based alloys, e.g. Monel®, but reactor modifications and maintenance cannot be done on the dry conversion reactors without welding on aged and thermal-cycled materials. Reactors cannot be quickly upgraded in the fluidized bed section except by welding new metal to modify the geometry. Welding on old materials such as Inconel® 625 or Monel® can cause problems with cracking at the welds between the aged and thermal-cycled reactor metal and the new sections. Unless the whole reactor is heat treated, cracking can occur at the weld seams since the aged thermal-cycled metal is dissimilar to the new metal which is more amorphous. Cracking will occur in a short time, typically soon after installation at the restart of operation. Any changes to a gas-phase reactor or a fluidized bed section of an existing reactor design, up to and including a full reactor replacement, are very expensive. Furthermore, although the entire reactor itself can undergo heat treatment, this is very costly and time consuming.
In addition, current reactors are limited to a fixed capacity and enrichment capability with respect to the gas-phase reaction section and the fluidized bed section. They cannot tolerate feeds greater than 5% enrichment without being replaced. These reactors cannot be upgraded unless the fluidized bed section or the gas-phase reaction section are cut out and new geometry sections are welded on, and these can fail from cracking at weld seams.